While visiting Ann Arbor, Michigan this summer, I got an upclose and personal view of pervious (porous) pavement. I have always been a fan of this type of pavement to counteract our “paving paradise to put a parking lot” philosophy and reduce our storm water run-off problem. You know. All the flooding associated with more pavement than grass?
So, What’s the Problem with Parking lots?
Parking lots and other impervious sites, such as driveways, sidewalks, and buildings, contribute to an increase of pollutants into our waterbodies. According to the EPA, stormwater runoff picks up the following:
“Sediment can cloud the water and make it difficult or impossible for aquatic plants to grown. Sediment also can destroy aquatic habitats.
Excess nutrients can cause algae blooms. When algae die, they sink to the bottom and decompose in a process that removes oxygen from the water. Fish and other aquatic organisms can’t exist in water with low dissolved oxygen levels.
Bacteria and other pathogens can wash into swimming areas and create health hazards, often making beach closures necessary.
Debris- plastic bags, six-pack rings, bottles, and cigarette butts – washed into waterbodies can choke, suffocate, or disable aquatic life like ducks, fish, turtles, and birds.
Household hazardous wastes like insecticides, pesticides, paint, solvents, used motor oil, and other auto fluids can poison aquatic life. Land animals and people can become sick from eating diseased fish and shellfish or ingesting polluted water.“
So how Does Pervious Pavement Help?
First, let’s clarify what is pervious or porous pavement. According to the Stormwater Manager’s Resource Center,
“Porous pavement is a permeable pavement surface with an underlying stone reservoir that temporarily stores surface runoff before infiltrating into the subsoil. This porous surface replaces traditional pavement, allowing parking lot runoff to infiltrate directly into the soil and receive water quality treatment. There are several pavement options, including porous asphalt, pervious concrete, and grass pavers. Porous asphalt and pervious concrete appear the same as traditional pavement from the surface, but are manufactured without “fine” materials, and incorporate void spaces to allow infiltration.” [Source.]
For years, I have known about porous pavement and was leery of the freeze and thaw issues that I thought could impact asphalt or concrete pervious pavements effectiveness. More northern climates are using this method to comply with city requirement of reducing storm water drainage as evidenced by my recent close encounter of the pervious pavement kind.
It is not too often you see cold climate pervious pavement installations. At least I haven’t seen them. However, in 2007, the University of New Hampshire installed a pervious pavement parking lot. UNH’s installation was one of the first major pervious pavement projects in New England. [Source.] Talk about testing it in a really cold environment.
Since 2004, UNH’s Storm Water Management Center was formed with a mission “dedicated to the protection of water resources through effective stormwater management.” Testing cold climate pervious pavement was just a natural progress in their stormwater management efforts.
Interested in installing cold climate pervious payment? See the Center’s 2009 guidelines for the installation of porous pavement.
But does it work?
Several winters later, UNH can dispel the myth that pervious pavement won’t work in cold climates. A 2008 article entitled “Pervious Pavement” stated
“However, according to Dr. Robert Roseen, director of the University of New Hampshire Stormwater Center (UNHSC), stormwater management systems using infiltration and filtration mechanisms, if properly designed, can work well in cold-weather environments. He has been leading a four-year research effort focused on monitoring the year-round performance of a porous asphalt placement that was installed on the UNH campus. In addition, the UNHSC is hoping to shed light on the functionality of pervious concrete by testing a large placement that was also installed on the university campus in August 2007—the first major pervious concrete parking facility in New England. The purpose and function of the UNHSC is to evaluate the range of stormwater treatments systems available to designers, including proprietary and nonproprietary systems.”
However, according to Stormwater PA,
“Pervious pavement is not recommended for high traffic areas because of the potential for clogging, nor is it a good idea for stormwater “hotspots” which generate highly contaminated runoff with a higher than usual concentration of pollutants. Areas of low soil permeability, seasonal high groundwater tables, and areas close to drinking water supply wells should also be avoided.”
Want to see pervious pavement in action? See the below video the demonstration of pouring 1500 gallons of water in five minutes on the pavement with very little runoff.
Cost and Maintenance
This system does not come without cost. Dr. Roseen, UNH Stormwater Center Director, stated that normal parking lots have a 12 to 15 year life in northern climates due to freeze/thaw. On the other hand, previous pavement can last over 30 years. The reconstruction of the UNH parking lot was much more costly than repaving; however, according to Roseen, the University will see a payback on its investment. [Source.]
“For new development, Roseen says that although material costs are approximately 20 to 25% more than those for traditional pavement, the total project cost for these systems with reduced stormwater infrastructure is comparable to standard pavement applications with which stormwater infrastructure is required.”
As for maintenance, see here for the Center’s winter and maintenance guidelines. What struck me in the maintenance guidelines was the reduction in deicing materials. The guidelines state,
“Up to ~75% salt reduction for porous asphalt can be achieved. Salt reduction amounts are site specific and are affected by degree of shading.
USE SALT REDUCTION NUMBERS WITH CAUTION!!!”
In addition, black ice, which is melted water that forms back into ice as the temperatures fall, is reduced with this type of application. The melted water drains through the pavement which alleviates black ice.
The Stormwater PA noted that cold climates pose challenges for this type of pavement and requires planning with regards to plowing, use of road salt and other maintenance. The agency further noted that failures of porous pavement usually arise during construction, so care must be taken in the installation of a pervious pavement project.
Concrete vs Asphalt
For more information about using concrete versus asphalt pervious pavement, see the article, “Pervious Pavement,” and USGBC’s article, “Improvement of Porous Pavement System for on‐site Storm Water Management.”
Does your town have a pervious pavement parking lot or road? If so, how has it fared?
Do you have a pervious pavement driveway? If so, how has it fared?
Thoughts about the cold climate pervious pavement?
Thoughts about concrete versus asphalt pervious pavement?
Does anyone have grass pavers? If so, thoughts?